Robust engineering of two-dimensional (2D) materials via covalent grafting of organic molecules has been a great strategy for permanently tuningtheir physicochemical behaviors toward electrochemical energy applications. Herein, we demonstrated that a covalent functionalization approach of graphitic surfaces including graphene by a graftable porphyrin (g-Por) derivative, abbreviated as g-Por/HOPG or g-Por/G, is realizable. The efficiency of this approach is determined at both the molecular and global scales by using a state-of-the-art toolbox including cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, atomic force microscopy (AFM), and scanning tunneling microscopy (STM). Consequently, g-Por molecules were proven to covalently graft on graphitic surfaces via C-C bonds, resulting in the formation of a robust novel hybrid 2D material visualized by AFM and STM imaging. Interestingly, the resulting robust molecular material was elucidated as a novel bifunctional catalyst for both the oxygen evolution (OER) and the hydrogen evolution reactions (HER) in acidic medium with highly catalytic stability and examined at the molecular level. These findings contribute to an in-depth understanding at the molecular level ofthe contribution of the synergetic effects of molecular structures toward the water-splitting process.

This paper describes an efficient approach to fabricate Fe-Porphyrin thin film deposited on highly oriented pyrolytic graphite substrate (HOPG/FePP) via the dip-coating method serving as a novel electrocatalyst for oxygen reduction reaction (ORR) in acidic medium. The electrochemical, morphological behaviors and surface structure at the molecular level of the HOPG/FePP as well as its catalytic activities were characterized upon employing a state-of-the-art toolbox including cyclic voltammetry (CV), atomic force microscopy (AFM), electrochemical scanning tunneling microscopy (EC-STM) and linear sweep voltammetry (LSV). Consequently, the HOPG/ FePP thin film exhibited a significantly enhanced catalytic activity for ORR under applied experimental conditions.

In this study, a novel functionalization protocol of highly oriented pyrolytic graphite (HOPG) was proposed, in which a two dimensional (2D) porous network formed by alkoxy-substituted dehydrobenzo[12]annulene (DBA-OC12) was served as a sacrificial template for electrografting of 3,5-terbutyl diazonium (3,5-TBD). The 2D DBA-OC12 porous network was synthesized by drop-casting of the corresponding precursor followed by a drying process. The structural and electrochemical properties of pristine as well as functionalized HOPG surfaces were investigated by means of cyclic voltammetry (CV) and scanning tunneling microscopy (STM).

Multilayered growth is often observed upon electrografting aryl diazonium derivatives on graphitic substrates due to the reactive nature of aryl radicals. The mechanism of the multilayer formation has been investigated either by measuring the thickness of the grafted layer, the charge transfer, or via simulations. Spectroscopy and in particular microscopy approaches are underrepresented. Herein, we demonstrate a comparative characterization of the multilayer growth of two diazonium derivatives on highly oriented pyrolytic graphite using a combination of cyclic voltammetry, atomic force microscopy, and scanning tunneling microscopy. While dendritic growth is observed for 4-nitro phenyl diazonium (4-NBD), 4-carboxy phenyl diazonium (4-CBD) shows layer-by-layer growth upon increasing the molecular concentration, revealing the impact of the functional groups on the growth mechanism.

A conventional route to create such nanoscale electronic devices using the autonomous ordering and assembly of organic molecules on atomically well-defined surfaces has been proposed. However, these thin films are unstable in realistic environments due to weak interaction between the organic molecules and crystal surfaces. Therefore, enhancing the interfacial interaction between them is assigned as the key approach to extend the scope of application of these promising monolayer thin films. In this work, we demonstrate the formation of an organic monolayer, namely 3,4,5-trimethoxy diazonium (3,4,5-TMD), on a Highly Ordered Pyrolytic Graphite (HOPG) electrode by using the power of electrochemical method. The structural properties at the nano scale as well as the bonding nature between 3,4,5-TMD adlayer and HOPG electrode at the interface were investigated by a combination of cyclic voltammetry (CV), atomic force spectroscopy (AFM) and Raman spectroscopy. As a result, the 3,4,5-TMD molecules covalently bond to carbon atoms located at the HOPG interface for forming a monolayer with its thickness of 0.92 ± 0.02 nm. This finding opens a partway to apply the electrochemical grafting for covalent functionalization of 2D materials on HOPG and other metallic surfaces.

Robust engineering the surface properties of layered materials is assigned as one of essential strategies for permanently improving their overall physicochemical behaviors towards high-end technology applications. In this regard, covalent functionalization of graphitic surfaces including graphene is performed upon electrografting of 4-(1H-1,2,4-triazol-1-ylmethyl) diazonium (4-TYD). The efficiency of this approach is determined by a state-of-the-art toolbox including cyclic voltammetry (CV), atomic force microscopy (AFM), scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), Kelvin probe force microscopy (KPFM) and Raman spectroscopy. The degree of the covalent functionalization is dependent on the molecular concentration of 4-TYD, in which the full monolayer is obtained upon electrografting with a 1 mM 4-TYD containing solution. The electrografted layer could be removed by thermal annealing leaving the pristine graphitic surfaces behind. This finding provides an efficient approach for robustly anchoring bioactive compounds onto graphene and other 2D materials in a controlled manner towards high-end technology applications.

Electrochemical reduction is considered as one of the simple and effective methods with respect to the CO2 conversion to value-added chemicals. With this regard, on the study of novel catalysts plays a crucial role for overcoming the chemical inertness and enhance the CO2 conversion efficiency. In this paper, nano Cu based highly efficient electrocatalysts for CO2 redution are developed by electrochemical deposition from the Cu2+ containing electrolyte. Crystalline structure and morphology of all synthesized Cu nanomaterials are characterized by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). Accordingly, all obtained Cu nanomaterials consist of both nanocuboid and dendritic features. The catalytic capability for CO2 reduciton of the fabricated Cu nanomaterials is determined upon using linear sweep voltametry (LSV) method. As a result, the sample electrodeposited for 240s exhibits the highest catalytic characteristics among others with the approximate efficiency of 85 % at the reduction potential of E = -0.5 V so với Ag/AgCl.

Nanoscale tuning of the surface properties of graphene-like materials is essential to optimize their application in electronic devices and protective technologies. The covalent modification method has recently been established as the most effective approach for tailoring the interface structure and properties, which are key aspects for fine-tuning the processability and performance of graphene-like materials. In this work, we demonstrate systematic exploration of the reversible covalent functionalization of a highly oriented pyrolytic graphite (HOPG) surface, a model system of multi-layered graphene, at the molecular scale. This is achieved using 3,5-trifluoromethyl benzenediazonum (3,5-TFD) and experimental investigations via cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), scanning tunneling microscopy (STM), and Raman spectroscopy. The degree of functionalization could be tuned by varying the concentration of 3,5-TFD dissolved in the grafting electrolyte. The covalently functionalized layer of 3,5-TFD was either locally degrafted by the STM tip or globally detracted upon thermal treatment, leaving the defect-free graphitic surfaces behind. Our findings open a new pathway for reversibly and robustly functionalizing graphene and other 2D materials for multiple uses in high-end applications.

Tuning the charge carier concentration of graphene is one of the key challenges in the field of graphene research. An effective solution for this is to dope graphene by organic molecules that physisorb or self-assemble on the graphene surface. Therefore, a comprehensive understanding of their surface structures at the molecular level is realy nessesary. In this contribution, we report on the role of the applied electrode potential in the adsorption/self-assembly of such n-dope molecule, dibenzyl viologen (DBV), on a highly oriented pyrolytic graphte (HOPG) surface (a multi-layer graphene material) determined by using a combination of cyclic voltametry (CV) and electrochemical scanning tunneling microscopy (ECSTM) methods. The obtained results reveal that dibenzyl viologen molecules can exist at three redox states corresponding to three respective adsorbate phases depending on the applied electrode potential. The DBV2+ molecucles physisorb and form disordered phase, whereas DBV·+ and DBV0 moleucles self-assemble forming dimer and stacking phases, respectively, on HOPG surface.

Molecular functionalization of graphitic surfaces with nanopatterned structures is regarded as one of the effective bottom-up techniques to tune their electronic properties towards electronics applications. Diazonium molecules have been often employed to covalently functionalize graphene and highly oriented pyrolytic graphite (HOPG) substrates. However, controlling the structure of the molecular adlayers is still challenging. In this contribution, we demonstrated an inconventional approach for covalent functionalization the HOPG surface by using mixture of 4-nitrobenzenediazonium (4-NBD) and 3,5-bis-tert-butylbenzenediazonium (3,5-TBD) molecules in which the former tends to polimezise and physisorb while the later chemically anchors on surface. The physisorbed features can be removed by washing with hot toluene and water. As a result, the HOPG surface is patterned in a quasi-periodic fashion. The efficiency of this development was verified by a combination of cyclic voltametry (CV) and atomic force microscopy (AFM) methods. This finding represents a convenient strategy for creating nanoconfined templates that might serve as nano-playgrounds for further supramolecular self-assembly and other on-surface reactions.

Despite holding unique electronic, optical, mechan-ical, and thermal properties, some inherent characteristics ofgraphene restrict its widespread use in technological applicationssuch as digital electronics. The introduction of ordered organicadlayers on top of graphene has been identified as a potentialapproach to tune its electronic band structure via quantumconfinement effects caused by molecular-scale ordering within theadsorbate layers. To this end, the redox-dependent self-assembledmolecular architectures of dibenzyl viologen (DBV) on graphiticsurfaces including graphene are investigated under electrochemicalcontrol. Molecular-resolution electrochemical scanning tunnelingmicroscopy results reveal three architectures, namely, the mobile,dimer, and stacking phases, corresponding to different DBV redox states, that is, DBV2+, DBV center dot+, and DBV0, respectively, formed andstabilized on both highly oriented pyrolytic graphite and chemical vapor deposition graphene on a copper foil. The phase transitionis fully controlled by the applied electrode potential. The patterned functionalization of graphitic surfaces via laterally confined self-assembly of DBV molecules was demonstrated. Thesefindings may help pave the way to functionalize graphene and other two-dimensional materials in both global and patterned manners by means of viologen-based self-assemblies.

Surface denaturation of carbon surfaces with molecular monolayer is appointed as one of the most effective bottom-up techniques to enlarge the applicability of the carbon-based electrodes in the electrochemical sensor field. Diazonium molecules have been often employed to denature the surface of materials such as graphite and graphene through the formation of C-C chemical bonds between them. However, the layered formation of these molecules is not well controlled yet due to their intrinsic high reactivity. This report demonstrated a practical approach for covalent functionalisation of the highly oriented pyrolytic graphite (HOPG) surface, a model system of multilayered graphene, by using 3,5-bis-tert-butylbenzenediazonium molecules. Due to the substituents at the 3,5 positions the aryl radicals prefer bonding directly to the HOPG surface than attacking the grafted aryls towards the monolayered formation. The efficiency of this approach was determined by the combined cyclic voltammetry, atomic force microscopy and scanning tunnelling microscopy.

In this contribution, a combination of cyclic voltammetry (CV), atomic force microscopy (AFM), electrochemical scanning tunneling microscopy (EC-STM) and Kelvin probe force microscopy (KPFM) is used to characterize the electrochemical, structural and electronic properties of the dibenzyl viologen (DBV) molecules based adlayers electrochemically deposited on highly oriented pyrolytic graphite (HOPG) surface. The adlayer formations on HOPG are dependent on its redox states in-situ modulated by the electrode potential and the used concentration. Relying on the intrinsic solubility of individual reduced molecules one enables permanent modulation the modification degree of HOPG surface. In addition, at the potentials where HOPG surface is merely modified by DBV0 molecules, the electrical properties of HOPG surface can also be modulated by various DBV2+ concentrations as the variable.

Doping of graphene by self-assembled molecular network of uncharged dibenzyl viologen (DBV0) generated in situ.

In this contribution, the electrochemciacl deposition method is used to synthesize uncharged dibenzyl viologen (DBV0) firm on HOPG surface. Electrochemical property and surface structure of the molecular adlayer are characterized by employing a combination of cyclic voltammetry (CV) and scanning electron microscope (SEM). Consequently, the DBV0 molecules generated from the reduction of the corresponding DBV2+ molecules at the solid/liqid interface by applying suitable electrochemical potentials are able to physisorb and form a physisorbed adlayer on HOPG. The existence of the DBV0 adlayer on HOPG surface is also confirmed by its blocking effect with respect to the electron transfer at the interface of electroactive [Fe(CN)6]2+ molecules.

In this respect, a combination of cyclic voltammetry (CV), Raman spectroscopy, and Atomic Force Microscopy (AFM) is employed to characterize the structural, electrochemical and electronic properties of diazonium thin layers covalently functionalized highly oriented pyrolytic graphite (HOPG) surface. As a consequence, a grafted layer thin film of 4-nitro-benzene-diazonium tetrafluoroborate (4-NBD) is formed on HOPG surface with an average thickness of about 3.5 ± 0.2 nm. A D-band peak appearrance at the wave length of 1336 cm-1 on the Raman spectrum indicates an enhancing of defects caused by covalent C-C bonds. A tentative model illustrating the formation of 4-NBD grafted multilayer governed by the dendritic mechanism is also proposed. This finding opens a new approach to control the degree of functionalization of graphitic surfaces and other 2D materials.

In this contribution, we provide a view on the role of halide interlayers in the self-assembly of layers of organic molecules at metal-electrolyte interfaces with molecular resolution. In particular, the ordering of tetra(4-trimethylammoniophenyl) porphyrin molecules in cationic form, abbreviated as [H(2)TTMAPP](4+), has been studied on a Cu(111) electrode surface in aqueous solution containing chloride-, bromide- or iodide-anions using a combination of cyclic voltammetry (CV) and in-situ electrochemical scanning tunneling microscopy (EC-STM). On the one hand the obtained results unveil that the degree of ordering of the self-assembled layer of [H(2)TTMAPP](4+) cations on the Cu(111) surface changes significantly when changing the halide anion in the working electrolyte, and, thereby, the buffer layer between the Cu(111) surface and the adsorbed [H(2)771VIAPP](4+) molecular cations. Under the same experimental conditions a fully ordered layer is observed on the chloride precovered Cu(111) surface, but less ordering and even incomplete monolayer formation are found on the bromide and iodide terminated Cu(111) surface, respectively; the degree of order decreases with decreasing electronegativity of the underlying halide. On the other hand potential driven reduction of the organic species lowers the charge density of the organic cations themselves causing a desorption of the reduced molecules at even lower potentials from any of the three differently halide modified electrode surfaces. Both observations underline the importance of electrostatic interactions in the adsorption and structure formation of the porphyrin molecules on the halide modified surfaces.

A convenient covalent functionalization approach and nanopatterning method of graphite and graphene is developed. In contrast to expectations, electrochemically activated dediazotization of a mixture of two aryl diazonium compounds in aqueous media leads to a spatially inhomogeneous functionalization of graphitic surfaces, creating covalently modified surfaces with quasi-uniform spaced islands of pristine graphite or graphene, coined nanocorrals. Cyclic voltammetry and chronoamperometry approaches are compared. The average diameter (45-130 nm) and surface density (20-125 corrals/μm2) of these nanocorrals are tunable. These chemically modified nanostructured graphitic (CMNG) surfaces are characterized by atomic force microscopy, scanning tunneling microscopy, Raman spectroscopy and microscopy, and X-ray photoelectron spectroscopy. Mechanisms leading to the formation of these CMNG surfaces are discussed. The potential of these surfaces to investigate supramolecular self-assembly and on-surface reactions under nanoconfinement conditions is demonstrated.

Highly oriented pyrolytic graphite (HOPG) can be covalently grafted with aryl radicals generated via the electrochemical reduction of 3,5-bis-tert-butyl-diazonium cations (3,5-TBD). The structure of the grafted layer and its stability under electrochemical conditions were assessed with electrochemical scanning tunneling microscopy (EC-STM) and cyclic voltammetry (CV). Stable within a wide (>2.5 V) electrochemical window, the grafted species can be locally removed using EC-STM-tip nanolithography. Using dibenzyl viologen as an example, we show that the generated nanocorrals of bare graphitic surface can be used to study nucleation and growth of self-assembled structures under conditions of nanoconfinement and electrochemical potential control.